Wink exposure control

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BugEZ
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Wink exposure control

Post by BugEZ »

On my stacking rig I don’t use strobe/flash, rather custom LED lights instead. My older Pentax camera bodies had lots of vibration from mirror and shutter motion. To counter this I used the two second delay mode (mirror up for two seconds prior to shutter actuation) and timed the LED drive to turn them all on ~.5 seconds after shutter opening, and then off slightly before the shutter closes. The shutter opening setting was normally two seconds. I built this LED timing logic into my rig controller. It worked great for many years.

Last year I transitioned to a mirrorless body (Pentax K-01) to eliminate the mirror delay. Unfortunately the new body did not have a direct hard wire connector for shutter activation so I had to build an IR optical trigger. What I discovered was that there was occasionally a brief delay between the IR trigger signal and shutter actuation. This interfered with the open loop timing of my LEDs and resulted in variable exposures as the LED “wink” did not always happed while the shutter was open.

After the expense of a camera purchase and trouble to build the IR shutter interface I was not very pleased with the results.

I rethought how I might interface the shutter and the LED trigger and control. Rather than triggering the lighting with the rig controller that sequences the stepper motor and shutter, I offloaded the LED control to a separate analog circuit triggered by the flash hot-shoe signals.

I found many pulse delay circuit designs on-line and customized one for my needs that interfaced nicely with my LED drive box. My circuit uses a dual 555 timer integrated circuit. There are two adjustable potentiometers that set the on delay (after trigger is detected) and the pulse duration. The exposures are uniform again.

The down side of this approach is the added clap-trap of another black box incorporated into my stacking gear. The up side is the ease of adjusting the “wink” by only turning one pot.

Keith

ChrisR
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Post by ChrisR »

If I'm understanding, you have a delay between the flash output signal and LED-ON, and a second delay to LED-OFF, with an analog knob setting to adjust each. And you're free of the need for an IR trigger.

Starting from scratch I think I'd use a couple of "ebay" modules with digital readouts to do that. There do exist industrial timer units which give a delay followed by a settable pulse in one box, but they're expensive by comparison.
I guess sod's law would mean a signal would be the "wrong way up" at some point, which may mean a little hacking.
But if yours works, well done I wouldn't fix it ;)

Having turned a Canon into a brick by connecting something, I'd be very wary with connections to a camera. Did you take precautions there?
Chris R

BugEZ
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Post by BugEZ »

ChrisR wrote:
you have a delay between the flash output signal and LED-ON, and a second delay to LED-OFF, with an analog knob setting to adjust each.
Yes exactly.

ChrisR also wrote:
And you're free of the need for an IR trigger.
No I still use the IR trigger. But now variation in the camera response to the IR trigger does not impact exposure.

A time delay module approach is certainly robust and if I had them in hand, I probably would have considered it. But I had the integrated circuit and enjoy tinkering with electronics. My experience with this sort of thing is that after I have an acceptable pot setting I don’t tinker with it much.

ChrisR also mentioned concerns of camera damage when hooking electronics directly to a camera. I must confess that this terrified me when I first made an intervalometer for my old Pentax. I followed instructions on a DIY website. When it was time to hook it up I placed large resisters in series with the home built circuit (goal being to avoid an over current event) and gradually swapped in smaller resisters till it triggered reliably, then soldered in resisters of that value. Perhaps I was lucky, but I never fried the camera. I copied the basics of the intervalometer design into the trigger circuit on my stacking controller. Were I to start from scratch I would use optical isolators to trigger a camera via a hard wired port. I saw optos used as a camera trigger on another DIY site and think this is a best practice.

K

Saul
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Post by Saul »

BugEZ wrote:...A time delay module approach is certainly robust and if I had them in hand, I probably would have considered it...
Maybe this would do ?
http://www.photomacrography.net/forum/v ... hp?t=35945
Saul
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ChrisR
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Post by ChrisR »

You would know best! I can't see a spec sheet for it.
There's a whole rash of timer modules on ebay now, I just checked. A new type with "18 modes" has just appeared, but the capabilities are poorly translated. One type has two timers together.

What signal can you trigger that timer with, Saul?

Complete Opto coupling of inputs is "impossible" if the output from the previous device, such as a camera hot shoe, doesn't supply any power. You need to illuminate a small LED inside the opto coupler.
If you supply that power from your box , then you aren't fully isolated. As Keith says, resistance/filtering helps.

Nikon's old 10 way connector had power on one pin, so one could use that. Otherwise, camera power supplies aren't accessible afaik.
I worry about earth loops, too. Maybe someone else has more experience of blowing things up... - ?
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Saul
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Post by Saul »

ChrisR wrote:...but the capabilities are poorly translated...
That's true, it took some time for me to get to the right setting :)
What signal can you trigger that timer with, Saul?
Correct me if I misunderstood your question

"Shutter signals from the WeMacro are controlling relays, which send the same signals to the camera and the start signal (4th photo) to the timer delay relay. LED lights are connected through the S0-S1 dry contacts. I'm also using simple switch in parallel to these contacts (not shown in photos) to override delay mode and for modeling purposes. Later will post connection diagram. "

NO dry contact of the relay are connected in parallel to the Restart button on the timer and launches timer cycle.

...and "LED lights are connected through the S0-S1 dry contacts" on the timer relay
Complete Opto coupling of inputs is "impossible" if the output from the previous device, such as a camera hot shoe, doesn't supply any power. You need to illuminate a small LED inside the opto coupler.
I'm not familiar well with hot shoe internals. If , let's say, you can pass through them 5-12v (like speedlight) & around 40mA ( not sure how much will be in speedlight case, never measured) - you could use directly simple relay with external power supply. If current should be less - you could use relay with optocoupler control input. i would go straight to the 2nd option, this kind of relays are widely available on ebay, like
https://www.ebay.com/sch/i.html?_from=R ... ay&_sop=15

If I remember correctly, current is ~5-10mA through the optocoupler. Just to make sure that through the hot shoe goes optocoupler signal only, not all current of optocoupler-relay assembly.
Last edited by Saul on Sat Dec 02, 2017 12:17 pm, edited 1 time in total.
Saul
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rjlittlefield
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Post by rjlittlefield »

Keith, for what it's worth I encountered a similar problem -- and developed a similar solution -- in the escapade described at Canon T1i: EFSC has large variation in shutter delay.

There could conceivably be some information in that discussion that would help your situation.

But I think the bottom line is that if you have something that works, the best use of time might be getting back to taking pictures!

--Rik

ChrisR
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Post by ChrisR »

I didn't see Keith asking a question or having a problem. The suggestion was to not change it. I assumed the post was to open a discussion.
The key advantage Keith has, because it's not a Canon, is a flash trigger output.

Saul - My question rephrased: is there a specification for the trigger? In parallel with a button, ok, but if that means "low", then below what voltage and with what impedance? Edge or level trigger? Do they give a circuit diagram?

Regarding the optocoupler, you're kinda missing the point I was trying to make. Yes it's very easy to light an led in an optocoupler, (or the coil of a relay) from a hot shoe contact, but you have to get the power from somewhere. Hotshoe contacts supply no power. All those I've seen, simply connect the centre contact to ground.
Damaging electrical signals go from one device to the other just as easily through ground or power lines if the wrong thing goes wrong.
Chris R

Saul
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Post by Saul »

ChrisR wrote:Saul - My question rephrased: is there a specification for the trigger? In parallel with a button, ok, but if that means "low", then below what voltage and with what impedance? Edge or level trigger? Do they give a circuit diagram?
They are giving nothing :)
And don't go too deep with electronics :) Like I mentioned - "NO dry contact of the relay are connected in parallel to the Restart button on the timer and launches timer cycle" - normally open dry contacts of the extra relay in parallel to the button, 4th photo - with relay contacts you just mimicking same Restart button which is starting timer's cycle.
Regarding the optocoupler, you're kinda missing the point I was trying to make. Yes it's very easy to light an led in an optocoupler, (or the coil of a relay) from a hot shoe contact, but you have to get the power from somewhere. Hotshoe contacts supply no power. All those I've seen, simply connect the centre contact to ground.
Damaging electrical signals go from one device to the other just as easily through ground or power lines if the wrong thing goes wrong.
Damned, my bad English, I'm not missing your point :) Sorry Chris , :) ...
Like I mentioned - " you could use directly simple relay with external power supply" - through the hot shoe contacts , limiting resistor, ext. power supply you feeding optocoupler's diod , which switches on the relay (these ebay relay assemblies has everything but power supply). And with relay contacts you controlling that timer delay(parallel to the button etc) relay or whatever else ... How you'll do with power supplies - it is different story - you can use 5v for optorelay and buy 5v timer delay relay. Or, if you are WeMacro user - use same 12v PS and buy 12v optorelay and 12v timer delay relay ...

Best way would be to draw a diagram, but ...too busy weekend :) Next week
Saul
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ChrisR
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Post by ChrisR »

Ah OK, I lost track of what was part of what ;).
A battery-powered intermediate would last ages if it only has to supply a few mA for the opto when the "flash" is fired.
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Saul
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Post by Saul »

ChrisR wrote:Ah OK, I lost track of what was part of what ;).
A battery-powered intermediate would last ages if it only has to supply a few mA for the opto when the "flash" is fired.
Exactly, even better than PS, less dangling wires ! :) :!: :idea:
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BugEZ
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Post by BugEZ »

To "close out" this thread, I went ahead and made a smooth copy of the schematic I used for my analog integrated circuit approach and some photos of the constructed circuit board.

The circuit is powered from the 5V bus of the same power supply that runs my stacking controller.

The interface adapter to the camera's hot shoe is made from a grocery store customer ID card, a thin credit card of sorts. I cut it down and folded it over to create moderate pressure on the center contact that signals when the camera wants to fire a strobe/flash. The ground lead wraps around the outside of the folded strip. Both contacts are quite secure (good enough for a rather tranquil studio) and the circuit has functioned reliably for thousands of exposures from last spring through the present.

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